1. Field of the Invention
This invention relates to a method and apparatus for making a pulley which may be used to transmit dynamic power. More particularly, the invention relates to a method and apparatus for making a pulley having a V-shaped groove in an outer surface thereof. Pulleys of this type are typically used with a belt having a trapezoidally-shaped cross section, for example as an electromagnetic clutch of a compressor in an automobile air conditioning system. The pulley made according to the method and apparatus of the present invention has an annular generally V-shaped groove in the outer surface thereof. The groove has a size and shape adapted to accommodate a transmission or other type of belt. The pulley is adapted to be attached, such as by welding, to a rotor or similar rotating device. Pulleys of this type will be referred to hereinafter as a "V-pulley".
2. Description of the Prior Art
Two alternative prior art methods for manufacturing V-pulleys are illustrated in FIGS. 1-4 and FIGS. 1, 5-7, respectively. In both of these prior art methods, a circular plate 10 is initially cut from a metal sheet 11 using a cutting punch 12 as shown in FIG. 1. Referring to the prior art method illustrated in FIGS. 1-4, the circular plate 10 is first formed into a cup 13a using a drawing die 14a. Cup 13a has a bottom portion 132a and a cylindrical portion 131a. Drawing with the drawing die 14a causes some thinning, primarily in the cylindrical portion 131a of cup 13a. Thus, the thickness t.sub.2 of cylindrical portion 131a is less than the original thickness t.sub.1 of plate 10. In a third manufacturing step, shown in FIG. 3, the cup 13a is further shaped by roller 16 which forms a generally V-shaped groove 153a in the cylindrical portion 131a. The V-shaped groove 153a comprises a bottom portion 152a and leg portions 151a. The action of the shaping roller 16 along the cylindrical portion 131a causes further thinning of the sheet material primarily in the vicinity of bottom portion 152a. Thus, the thickness t.sub.3 of portion 152a is less than thickness t.sub.2. In the final step of manufacturing, as shown in FIG. 4, a central portion of the V-pulley 15a is punched out by cutting punch 18. The V-pulley 15a is thus adapted to be mounted on a rotor or other type of rotatable shaft by extending the rotor or shaft into the punched out opening.
An alternate prior art manufacturing method is illustrated in FIGS. 1 and 5-7. In this method, the circular plate 10 is drawn with a drawing die 14b as shown in FIG. 5. Similar to the operation illustrated in FIG. 2, the drawing die 14b forms circular plate 10 into a cup 13b having a bottom portion 132b and a cylindrical portion 131b. However, the diameter of drawing die 14b is less than the diameter of drawing die 14a. Drawing with the smaller diameter die 14b causes a significant reduction in the thickness of the sheet material. Accordingly, the thickness t.sub.4 of cylindrical portion 131b is less than either the thickness t.sub.1 of the circular plate 10 or the thickness t.sub.2 of cylindrical portion 131a. As shown in FIG. 6, cup 13b is formed into a V-pulley 15b by the press 17. The press 17 forms a generally V-shaped groove 153b in the cylindrical portion 131b. The V-shaped groove 153b includes a bottom portion 152b and two leg portions 151b. In the last manufacturing step illustrated in FIG. 7, a central portion of the V-pulley 15b is cut using a cutting punch 18.
There are several disadvantages to the above-described prior art manufacturing methods. One disadvantage is the waste material 19 which remains after the initial cutting of the circular plate 10. This results in higher material costs.
Another disadvantage to the prior art manufacturing methods is that they require at least four separate manufacturing steps ((1) cutting, (2) drawing, (3) groove shaping and (4) punching) in order to form the V-pulley.
A still further disadvantage of the prior art manufacturing methods is the thinning of the sheet material in the vicinity of the bottom of the V-shaped groove. The bottom of the V-shaped groove must be able to withstand the tension of a belt wrapped around the pulley and carried within the V-shaped groove. Thinning of the bottom portion of the V-shaped groove leads to a reduction in the strength of the pulley which can lead in extreme cases to V-pulley failure.